Influence of intracerebroventricular administration of dopaminergic drugs on morphine state-dependent memory in the step-down passive avoidance test

The effects of dopaminergic drugs on morphine state-dependent memory of passive avoidance task were examined in mice. Pre-training administration of morphine (5 mg/kg) led to state-dependent learning with impaired memory retrieval on the test day which was reversed by pre-test administration of the same dose of the opiate. The pre-test intracerebroventricular (i.c.v.) administration of the dopamine D1 receptor agonist (SKF38393), dopamine D2 receptor agonist (quinpirole) and dopamine D2 receptor antagonist (sulpiride) not only reversed the effect of pre-training morphine treatment, but also increased this action of the drug. Furthermore, the pre-test i.c.v. administration of dopamine D1 receptor antagonist (SCH23390) prevented the restoration of memory by morphine. In conclusion, the morphine-induced recovery of memory, on the test day, seems to be induced, at least in part, through dopamine receptors.